The speed at which selected reactants are reaching active sites grafted on porous silica gels of various nature and porosity was evaluated using some model systems:  protonation of aminopropyl-grafted silica (APS), mercury(II) binding on mercaptopropyl-grafted silica (MPS), and accumulation of copper(II) on APS. Data were obtained from batch experiments, by monitoring the consumption of reactant in solutions containing the solid phases as dispersed particles (average size:  60−150 μm). Various grafted solids were studied, with pore diameter ranging between 4 and 15 nm and organic group contents of typically 1.4−1.9 mmol g-1. Diffusion processes in the porous organically modified silicas were found to be dramatically restricted as compared to those observed in homogeneous solution (≈103−104 times slower). They were dependent on several factors such as the pore size of the material and the size of the reactant, the density of grafted organic sites, and the nature of the starting silica gel. Evaluation of apparent diffusion coefficients was achieved by applying a simplified model based on spherical diffusion. This has allowed us to point out a significant decrease in the access rates upon gradual completion of reactions:  as the reactant concentration in the vicinity of increasing amounts of grafted groups is raised progressively, there is less room available in the porous structure to enable the probe to reach rapidly the remaining active sites. The apparent diffusion coefficient was found to drop dramatically after typically 30−50% reaction completion, depending on the nature of the probe. This study allows highlighting the optimal conditions that should be required to ensure efficient application of grafted silica gels, that is, in the fields of catalysis or heavy metal extraction.

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The insecticidal activities of essential oil extracts from leaves and flowers of aromatic plants against fourth-instar larvae of the mosquito Culex pipiens molestus Forskal were determined. Extracts of Myrtus communis L were found to be the most toxic, followed by those of Origanum syriacum L, Mentha microcorphylla Koch, Pistacia lentiscus L and Lavandula stoechas L with LC50 values of 16, 36, 39, 70 and 89 mg litre-1, respectively. Over 20 major components were identified in extracts from each plant species. Eight pure components (1,8-cineole, menthone, linalool, terpineol, carvacrol, thymol, (1S)-(-)-alpha-pinene and (1R)-(+)-alpha-pinene) were tested against the larvae. Thymol, carvacrol, (1R)-(+)-alpha-pinene and (1S)-(-)-alpha-pinene were the most toxic (LC50 = 36-49 mg litre-1), while menthone, 1,8-cineole, linalool and terpineol (LC50 = 156-194 mg litre-1) were less toxic.

The interactions of iodide ions with cuprite (Cu2O) surfaces were studied by combining batch experiments and surface analyses. The evolution of iodide uptake with pH was investigated. The thermodynamical calculations and surface analyses (X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy, and electrochemistry) were used to show that two different pH-dependent mechanisms are responsible for the accumulation of the iodide species on Cu2O. At pH values lower than 6.5, the precipitation of CuI occurs on the cuprite surface, while in more alkaline medium, the iodide adsorption takes place by substituting the surface hydroxyl groups of Cu2O. The sorption processes were not affected by a 1000-fold excess of chloride ions, but they were limited to the potential range corresponding to the stability domain of Cu2O (i.e., between −10 and +190 mV/ENH at pH 8); thus no accumulation was observed either on metallic copper or on CuO.